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High Level Nova Architecture Review – Flags and Services

Joseph Heck has written an excellent blog post on the Nova high level architecture for flags and services. Here is the intro:

I’ve been doing a lot of spelunking into the nova codebase, digging around and trying to learn some of the under pinnings. Some of these pieces were a bit confusing to me, so I’m stashing them up here for Google to find and share with others in the future.

Before I dive into the gritty details, it’s worth getting a high level overview so that some of this (hopefully) makes sense. OpenStack’s service architecture is made up of services that all talk with each other to get things done. nova-network, nova-scheduler, etc. There’s a lot of underpinning in the nova codebase to make those services relatively easy to write and work together – I was mostly curious about how they passed messages back and forth. As I dove in, the two pieces that stood out as needing to be understood first were the unified service framework in nova and configuration using flags (which it heavily depends upon).